What are the reliability limitations of keyspace notifications that developers should understand before relying on them for critical application logic?

Intermediate

Answer

Keyspace notifications are delivered using Redis's Pub/Sub mechanism, which does not guarantee delivery, meaning if a subscribing client is disconnected or too slow to keep up when a notification is published, that specific notification is simply lost forever, making keyspace notifications unsuitable for critical logic that absolutely must never miss an event.

-- If no subscriber is actively listening when a key expires,
-- that specific expiration event is lost forever
SUBSCRIBE __keyevent@0__:expired

Real-world example A team initially relied on keyspace notifications to trigger a critical billing calculation, then redesigned their system after realizing a brief subscriber disconnection had caused several important events to be silently missed.

Common follow-ups: What alternative approaches provide guaranteed delivery instead of Pub/Sub based notifications?;How do you detect if your application has missed keyspace notifications?

Streams;Pub/Sub

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